A "cowl flap" need not be a flap, or extend very far into the airstream, or require much mechanical power to open or close.
Original implementation was powered with the smallest Firgelli linear actuator(L12). It was powerful enough given the linkage design, but developed internal freeplay over time, assumed due to temperature. It's now powered with the familiar trim servo.
The lower cowl itself required the addition of reinforcement ribs, as shrinking the exit raises lower cowl pressure, and the entire cowl tries to blow itself into a round balloon shape, and this system requires cutting a pretty good size hole. The deformation didn't allow full closure, as seen here in the first video. Note the gap increase at 180 knots as compared to 120. It's a direct response to increased cowl pressure.
BTW, while there, note the disturbed flow when open, just aft of the rear slot, and just in front of the tailpipe. That's the disadvantage of anything extending into the airstream. As a flap gets larger and/or the open angle gets more acute, the disturbance gets larger. Pure drag. Everything goes smooth, including the tufts in the primary exit, as the auxiliary exits close and primary exit velocity rises. A slot exit like this one would produce less drag when open, thus there is less airspeed delta, open vs closed. The pitch trim change is very small.
A center hinged door means one of the two auxiliary exits is a recessed slot.
This video taken after internal cowl reinforcement, to check for full closure. Didn't bother with tufts, as the first video told me all I needed to know on that score:
Folks who are adding Nimmo's flaps while retaining a full size stock exit don't need to worry much about cowl deformation due to internal pressure. On the other hand, I've never videoed one at 180 knots.